Maybe something simpler. For example putting OT (off topic) in the subject
if it is appropriate. Also I think it is a good idea to state the age or
grade level your dealing with when talking about issues (everyone usually
does this when asking about or giving lesson plan information). Sometimes
when we've all gotten upset with each other over different education issues
and the real problem was the different situations especially different age
levels we were dealing with.

I am also our district's K-2 Librarian, and when I was first given this
position I joined a library listserv. They use codes, and there were good
points and bad points to using them. If it was a joke, then in the subject
you would put Humor: Jokes for Teachers. Other headings included Primary,
Elementary, High School, Tech, Misc.
Alot of the librarians had folders that their filters (I'm not a techy, this
is just what they told me). Their computers sorted their mail into folders
and subjects they weren't interested in were deleted without opening the
folder. Unfortunately, they were very picky about their labels, and I'm sure
they lost several people due to the flaming new members received if they
didn't use the labels. And that list was HUGE (over 10,000 members, which is
why I had to choose lists - you think WE talk alot! *L*)
Michal